Clarifying misunderstandings regarding vegetation self‐organisation and spatial patterns of fairy circles in <scp>N</scp>amibia: a response to recent termite hypotheses

Getzin, Stephan; Wiegand, Kerstin; Wiegand, Thorsten; Yizhaq, Hezi; Hardenberg, Jost von; Meron, Ehud

doi:10.1111/een.12267

Cited by 26 publications

(77 citation statements)

References 35 publications

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“…3H and SI Appendix, Tables S1 and S3). As also reported for Namibia (16), this below-average size of closely located FC areas is equivalent to a significant increase in the vegetation coverage, because the grasses then benefit from the higher density of the water-supplying gaps. Finally, it is remarkable that the proportion of Voronoi tiles with six corners is in all analyzed plots the largest, 46.9% on average, which is nearly identical to the 43-46% found in three different regions of Namibia.…”

Section: Resultssupporting

confidence: 68%

“…Finally, it is remarkable that the proportion of Voronoi tiles with six corners is in all analyzed plots the largest, 46.9% on average, which is nearly identical to the 43-46% found in three different regions of Namibia. This also indicates the dominance of hexagonal FC spacing in both ecosystems (16).…”

Section: Resultsmentioning

confidence: 63%

“…This is because the mechanism of water transport in the Namibian ecosystem with porous sand is soil-water diffusion, whereas in the Australian ecosystem with hard clay pans, it is overland-water flow. The sandy gaps in the Namibian ecosystem form large below-ground water reservoirs that sustain the surrounding water-consuming vegetation by soilwater diffusion (13,15,16). By contrast, the Australian FC gaps act as above-ground hard clay pans that produce runoff toward the surrounding vegetation matrix.…”

Section: Resultsmentioning

confidence: 99%

“…Several competing hypotheses exist ranging from vegetation self-organization (13)(14)(15)(16)(17), termite-induced activity (18), and Euphorbia poisoning (19) to abiotic gas leakage (20). Among these, vegetation self-organization stands out as the most solid mechanism that explains the emergence of large-scale order (15,16) and the strong dependence of fairycircle distribution on mean annual precipitation (13). Furthermore, only self-organized biomass-water feedbacks can explain the shrinking in size and disappearance of fairy circles after aboveaverage rainfall years and the typical enlargement and increased appearance of FCs after below-average rainfall years (21).…”

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confidence: 99%

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Discovery of fairy circles in Australia supports self-organization theory

Getzin

Yizhaq

Bell

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Vegetation gap patterns in arid grasslands, such as the "fairy circles" of Namibia, are one of nature's greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomasswater feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil-water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass-water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.drylands | spatial pattern | Triodia grass | Turing instability | vegetation gap P attern-formation theory (1) and the influence of Alan Turing's work on understanding biological morphogenesis (2) are increasingly recognized in environmental sciences (3). Vegetation patterns resulting from self-organization occur frequently in waterlimited ecosystems and, similar to Turing patterns, show pattern morphologies that change from gaps to stripes (labyrinths) to spots with decreasing plant-available moisture (4-6). The patterns may emerge on completely flat and homogeneous substrate and are induced by positive feedbacks between local vegetation growth and water transport toward the growth location.

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Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Discovery of fairy circles in Australia supports self-organization theory

Getzin

Yizhaq

Bell

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

167

215

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“…To the unfamiliar, it may be difficult to realize that plant populations can organize themselves into geometric order so as to optimize their access to scarce soil water (4)(5)(6). Based on the preliminary data obtained by excavating two gaps from the fairy circle (FC) area near Newman, Walsh et al (7) claim that subterranean termitaria are the sole cause of the Australian FCs (8).…”

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confidence: 99%

Reply to Walsh et al.: Hexagonal patterns of Australian fairy circles develop without correlation to termitaria

Getzin

Yizhaq

Bell

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Ecohydrological interactions within “fairy circles” in the Namib Desert: Revisiting the self‐organization hypothesis

et al. 2017

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Vegetation patterns such as rings, bands, and spots are recurrent characteristics of resource‐limited arid and semiarid ecosystems. One of the most recognizable vegetation patterns is the millions of circular patches, often referred to as “fairy circles,” within the arid grassland matrix extending over hundreds of kilometers in the Namib Desert. Several modeling studies have highlighted the role of plant‐soil interactions in the formation of these fairy circles. However, little is known about the spatial and temporal variabilities of hydrological processes inside a fairy circle. In particular, a detailed field assessment of hydrological and soil properties inside and outside the fairy circles is limited. We conducted extensive measurements of infiltration rate, soil moisture, grass biometric, and sediment grain‐size distribution from multiple circles and interspaces in the Namib Desert. Our results indicate that considerable heterogeneity in hydrological processes exists within the fairy circles, resulting from the presence of coarser particles in the inner bare soil areas, whereas concentration of fine soil occurs on the vegetated edges. The trapping of aeolian and water‐borne sediments by plants may result in the observed soil textural changes beneath the vegetation, which in turn, explains the heterogeneity in hydrological processes such as infiltration and runoff. Our investigation provides new insights and experimental data on the ecohydrological processes associated with fairy circles, from a less studied location devoid of sand termite activity within the circles. The results seem to provide support to the “self‐organization hypothesis” of fairy circle formation attributed to the antiphase spatial biomass‐water distributions.

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Clarifying misunderstandings regarding vegetation self‐organisation and spatial patterns of fairy circles in Namibia: a response to recent termite hypotheses

Cited by 26 publications

References 35 publications

Discovery of fairy circles in Australia supports self-organization theory

Discovery of fairy circles in Australia supports self-organization theory

Reply to Walsh et al.: Hexagonal patterns of Australian fairy circles develop without correlation to termitaria

Ecohydrological interactions within “fairy circles” in the Namib Desert: Revisiting the self‐organization hypothesis

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